Recently, dust cores that exhibit excellent magnetic characteristics over a broad frequency range have been increasingly used instead of electromagnetic steel plates in production of solenoid valves and motors. Such dust cores and a production method thereof are disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2002-246219 (Patent Document 1). According to the method of producing dust cores disclosed in Patent Document 1, atomized iron powder covered with a phosphate film is first mixed with a predetermined amount of polyphenylene sulfide (PPS resin) and then subjected to a pressure-forming process. The resulting compact is heated in air at 320° C. for one hour and then heated at 240° C. for another hour. The compact is then cooled to produce a dust core. The powder compact, which is obtained by pressure-forming of iron powder, may be used also as a structural material in production of mechanical components and others besides the magnetic components described above. Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-246219